Alan Turing's 1936 paper ON COMPUTABLE NUMBERS, introducing the Turing machine, was a landmark of twentieth century thought. It provided the principle of the post-war electronic computer. Influenced by his crucial codebreaking work in thesecond world war, Turing argued that all the operations of the mind could be performed by computers. His thesis, made famous by the wit and drama of the Turing Test, is the cornerstone of modern Artificial Intelligence. Andrew Hodgesgives a fresh and interesting analysis of Turing's developing thought, relating it to his extraordinary life.